The Yellowstone Valley spans USDA hardiness zones 4a-4b — a band that supports both cool-season staples and warm-season crops chosen to fit the local frost window.
Montana's longest growing season sits at its coldest-looking zones. The Yellowstone River bottomland from Billings down to Sidney runs 153-166 frost-free days (county_data.json) across USDA zones 4a-4b — a genuinely longer window than the state's 5a-6a mountain valleys, which sit in warmer zones but freeze sooner (Gallatin 114, Madison 117, Ravalli 146 frost-free days). That long, irrigated plains river-bottom season is what carries the corridor's sugar beets, corn, and full-season vegetables, and it is a distinctly different growing experience from Montana's SW/NW mountain valleys or the Hi-Line that a statewide average flattens away. The conditions favor potato, lentil, rhubarb, and cherry, among others — though every individual site edits that list with its own soil, sun, and drainage.
The Yellowstone Valley spans Montana.
Your yard isn't all of the Yellowstone Valley.
The Yellowstone Valley spans USDA zones 4a-4b, but your parcel sits in exactly one — and slope, tree cover, and low spots nudge it further. Enter your address and we'll score 1,086 plants against your land's actual soil, sun, and frost.
We read public map data around The Yellowstone Valley — soil, climate, flood, and parcel records. How we handle your address.
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The Yellowstone Valley — the short answer
The Yellowstone Valley: USDA zones 4a-4b, 153–166 frost-free days, in Montana.
- USDA zones
- 4a-4b
- USDA PHZM 2023, aggregated over the footprint
- Frost-free season
- 153–166 days
- NOAA Regional Climate Centers ACIS, 1991-2020
- Counties
- 7
- US Census TIGER/Line 2025
- Region type
- County cluster
- Growable Ground growing-region registry
Region boundary: Growable Ground growing-region registry — curated county clusters, EPA Level III ecoregions, and town clusters drawn finer than any county. Where a region publishes no measured season, no season figure is shown.
Hardiness Zone Range
What Grows in the Yellowstone Valley
Plants matched to the Yellowstone Valley's USDA zones 4a-4b, ordered by how much hardiness margin each has across the region — the ones with room to spare at both ends of this band lead. Each links to its full growing profile.
Native Plants of the Yellowstone Valley
Plants the USDA PLANTS Database documents as native and present in this region’s state, kept only where the published hardiness range meets the Yellowstone Valley’s USDA zones 4a-4b — closest range match first. Presence is recorded by state, so a plant can be documented across the state and still be scarce in your corner of the region.
The ground across the Yellowstone Valley
The USDA soil survey maps this ground county by county. These are those records weighted by land area across seven member counties — this region’s own profile, not a state figure.
The ground is predominantly Entisols, at 40% of mapped acres, followed by Inceptisols (30%), Mollisols (15%) and Alfisols (7%). Six soil orders appear somewhere inside the footprint, which is the honest reason a regional soil answer only goes so far. The most extensive named soils are Cabbart, Cambeth, and Lonna.
92% of those acres are well drained, and another 2% excessively drained, 1% somewhat excessively drained. Topsoil pH runs 7.2–7.9 between the lowest and the highest county on record.
Soil order
Entisols
Drainage
Well drained
Topsoil pH
7.2–7.9
Hydric soils
1%
Soil changes across a driveway, so which of these your own ground sits on is a parcel question rather than a regional one. Richland County holds the most wetland ground here, at 2% — soil types explained.
USDA NRCS SSURGO via Soil Data Access
What this means for growing in the Yellowstone Valley
The soil survey reads this ground county by county, and the readings above are those records summed across the Yellowstone Valley. Here is what they mean for a garden here — and the move an experienced grower makes about each one.
Drainage
From county records92% of the mapped acres across the Yellowstone Valley are well drained — ground that drains quickly. That is area-weighted across all seven of its mapped counties.
The upside is soil you can work early in spring and roots that never drown; the cost is that fast-draining ground dries out fast and leaches nutrients away before plants can use them.
Work in compost and mulch to hold moisture and feed, and water more often in short doses than deep and rarely.
USDA NRCS SSURGO
Surface pH
From county recordsTopsoil across the Yellowstone Valley runs pH 7.2–7.9 — alkaline in all seven of them.
Many vegetables cope, but acid-lovers like blueberries struggle, and iron and manganese lock up above about pH 7.5 — leaves yellow between the veins even in rich soil.
Elemental sulfur and generous organic matter lower pH slowly for the beds that need it; test first so you add only what the soil actually calls for.
USDA NRCS SSURGO
Safe to Grow Here?
What the federal record shows across the Yellowstone Valley — and how to grow with it.
Across the Yellowstone Valley's 7 counties the federal record holds 3,093 documented sites, mostly Nitrate (1,608), Underground Storage Tanks (921) and Brownfields (443). The heaviest single county is Yellowstone County, with 1,232.
That is a regional count, not a reading of any one lot — proximity to a documented site is information, not a diagnosis. Open the map outlined to the Yellowstone Valley to see which records sit where you actually grow.
Sources Checked
Summed across the 7 counties in the Yellowstone Valley
A note from Gnorman
What an experienced grower watches for around here
In and around the Yellowstone Valley, two things run higher than the national average across the 7 counties in the Yellowstone Valley — CAFO (55 sites) and Nitrate (1,608 sites). It's not cause for alarm — it's worth knowing, and there's a sensible way to grow around it.
CAFO: CAFOs pose a different contamination profile than chemical sources.
Nitrate: Nitrate contamination primarily comes from agricultural fertilizer runoff and failing septic systems.
Wash all produce consumed raw thoroughly, especially leafy greens grown near CAFOs.
Test well water for nitrate if you rely on a private well for irrigation (EPA standard: 10 mg/L).
Sources: EPA, USGS — 1.8M documented sites tracked nationwide across 9 federal source types.
Your land is one point inside the Yellowstone Valley
Everything above resolves to the Yellowstone Valley as a whole — a footprint spanning USDA zones 4a-4b. Your parcel sits in exactly one of them. Slope, tree cover, a low spot that pools cold air, and what is in the soil are all resolved at the address, and none of them are visible at region scale. That is the honest boundary of this page, and the reason the next step is a reading of your own ground rather than a better regional average.
Your Lot vs the Yellowstone Valley Average
Yellowstone Valley Average
- ●USDA Zones 4a-4b, averaged across Yellowstone Valley
- ●One soil character for all of Yellowstone Valley
- ●State-average frost dates
YOUR Parcel
- ✓Your exact zone, not Yellowstone Valley's 4a-4b
- ✓Your SSURGO soil type & pH
- ✓Your sun exposure, cast in 3D
See MY Growing Report
Read your parcel in the Yellowstone Valley
Pull a site-specific report for your exact address in the Yellowstone Valley — soil, sun, drainage, frost risk, contamination, and scored plant recommendations.
Three things about your lot that Yellowstone Valley averages can't show:
We read public map data around The Yellowstone Valley — soil, climate, flood, and parcel records. How we handle your address.
25+ data sources read at your address, not the Yellowstone Valley average
How we know this about the Yellowstone Valley
The boundary: a cluster of neighboring counties. Growing regions have no official boundary, so this footprint is our published one, and every figure on this page was measured over the counties inside it rather than borrowed from the state around it.
The datasets: hardiness from the USDA ARS Plant Hardiness Zone Map 2023, aggregated across the footprint; the growing season from NOAA Regional Climate Centers ACIS 1991–2020 28°F normals, read at each member’s own record; boundaries from US Census TIGER/Line 2025; the contamination record from the federal sources named in that beat above; the soil from the USDA NRCS SSURGO survey, read at each member county’s own record and weighted to this footprint by land area. Where a member carries no record of its own, it is absent from the figure rather than filled in.
Common questions about the Yellowstone Valley
What hardiness zone is the Yellowstone Valley?
The Yellowstone Valley spans USDA hardiness zones 4a-4b, aggregated from the USDA Agricultural Research Service Plant Hardiness Zone Map 2023 across the region's counties. Zones reflect average annual extreme minimum temperatures from 1991–2020 data.
How long is the growing season in the Yellowstone Valley?
Measured between 28°F hard freezes, the Yellowstone Valley's counties mostly run 155 to 166 frost-free days, median 158 (NOAA Regional Climate Centers ACIS, 1991–2020, over 7 member counties). That 11-day spread is the honest read — no single season describes 7 counties, and each county guide below carries its own.
When does frost risk end in the Yellowstone Valley?
Across the Yellowstone Valley, the middle half of member counties see their last 28°F hard freeze between Apr 28 and May 2 (median May 1), and their first fall freeze between Oct 4 and Oct 9. Those are hard freezes, not the last light frost: tender transplants wait for about May 22, and elevation decides which end of a 4-day spread you garden in.
What grows well in the Yellowstone Valley?
The Yellowstone Valley's conditions suit plants such as Potato, Lentil, Rhubarb, Cherry, Ponderosa Pine. What actually thrives on any one site still turns on its specific soil, sun, and drainage — we score each plant against the real conditions at your address.
How is the Yellowstone Valley defined?
The Yellowstone Valley is defined here as a curated cluster of 7 neighboring counties that share a growing character. Growing regions have no official boundary, so this footprint is our published one — every county in it is named on this page.
Which states does the Yellowstone Valley cover?
The Yellowstone Valley spans Montana. Each state's full growing guide is linked on this page.
What other growing regions cover the same states?
The Hi-Line, The Rocky Mountain Front / Great Falls Chinook Belt, Bitterroot Valley, Flathead Valley, Gallatin Valley, and Paradise Valley share at least one state with the Yellowstone Valley. Growing regions overlap and interlock — a single address can sit inside more than one, which is why the precise read is always the parcel, not the region.
What this page reads at the Yellowstone Valley’s own scale
6 of the readings below were taken at the Yellowstone Valley's own scale — the zone 4a-4b band across its footprint, a median 158-day season across its 7 counties and 3,093 documented federal contamination records across its 7 counties, 1,232 of them in Yellowstone County alone; one is borrowed from a wider read, named and linked below.
Measured here
- The USDA hardiness band 4a-4b aggregated across all 7 counties in the footprintUSDA PHZM 2023
- The boundary itself — the 7 counties this region is curated fromGrowable Ground subregion registry
- The growing character that makes this region distinct from the states it crossesGrowable Ground subregion registry
- The 28°F season across the footprint — the middle half of its 7 counties run 155 to 166 frost-free days, median 158NOAA Regional Climate Centers ACIS, 1991-2020
- The federal contamination record over the whole footprint — 3,093 documented federal contamination records across its 7 counties, 1,232 of them in Yellowstone County aloneEPA, USGS and USDA federal site records
- The soil order mix across the footprint — 40% Entisols, topsoil pH 7.2–7.9, area-weighted across its 7 mapped countiesUSDA NRCS SSURGO
Inherited from a wider read
- The candidate plant list — its state's curated sets, merged and filtered to zones 4a-4bfrom Montana
What this page can’t tell you
- Which end of the 11-day range your ground sits at — 155 days at one extreme, 166 at the other, decided mostly by elevationfrost dates explained →
- Which of those soils your own ground sits on — the survey maps them county-wide, and they change across a drivewaysoil types explained →
- The soil pH, drainage, sun hours, and frost pockets on one specific lotwhy one lot differs from the next →
Explore the Yellowstone Valley
State growing guides
Counties in this region
Other growing regions across Montana
Montana's coldest, driest strip — the northern-border county tier along US Highway 2 and the BNSF (old Great Northern) line — and the only Growable Ground region reaching USDA zone 3b: the Daniels–Sheridan–Roosevelt corner sits at 3b with just 142–146 frost-free days, a full zone colder than the 5a–6a mountain valleys captured elsewhere in the state. The western and central counties run 4a with 140–159 frost-free days. This is semi-arid dryland-wheat country with extreme winter minima and wide day-to-night diurnal swings; chinook winds moderate only the Glacier–Toole western end, leaving the shortest, most cold-hardy growing palette anywhere in Montana. None of that growing reality is visible on the sprawling statewide page.
Where the northern plains slam into the Rocky Mountain Front, chinook winds rewrite the rules of a zone-4 winter. Great Falls earns its "banana belt of the north" name because these warm, dry downslope gales can lift a February morning tens of degrees in an hour — sparing tender crowns the deep cold the Hi-Line just east endures. The same wind is the catch: it desiccates exposed evergreens and perennials and whipsaws plantings through thaw-freeze cycles that split bark and heave roots. Here the decisive question isn't your zone (4a–4b, roughly 140–159 frost-free days) but your parcel's exposure to the Front — which slopes, shelterbelts, and wind-lees the chinook finds, and which it spares.
The Bitterroot Valley runs roughly 95 miles along the Bitterroot River between the Bitterroot Range and the Sapphire Mountains, spanning Ravalli and Missoula counties (USGS) across USDA hardiness zones 5b-6a, where a short 137-to-146-day frost-free season closes early: both counties typically see first frost by late September.
A mountain-ringed northwest Montana valley whose big lake buffers the cold — sweet cherries on the lakeshore benches, with mint, grain, and hay on the valley floor.
Southwest Montana's Gallatin Valley, the Bozeman-area basin, sits in USDA zone 5a with a short ~114-day frost-free growing season — the last spring frost typically holds until early June and the first fall frost returns by late September.
Paradise Valley traces the Yellowstone River through Montana's Park County, where USDA zone 5a and a roughly 125-day frost-free season — last frost in late May, first frost in late September — shape a short, high-elevation growing window.